Rodrigo Martins

This paper deals with a new process to improve the stability of a-Si:H pin solar cells deposited in a single batch process by proper passivation of the interfaces. The process consists in removing partially a deposited sacrificial oxide layer grown between the p/i or i/n interfaces by SF6 etching. This layer is an absorber of defects and impurities that are introduced in the interfaces, mainly from the chamber walls and the substrate surface. The results achieved in laboratory samples lead to devices in which the fill factor and short circuit current density were improved respectively towards 75% and 16.5 mA cm-2, with a final working efficiency of about 9.5%. © 2001 Elsevier Science Ltd. All rights reserved.

This paper discusses the electron transport in the n-type amorphous indium-zinc-oxygen system produced at room temperature by rf magnetron sputtering, under different oxygen partial pressures. The data show that the transport is not band tail limited, as it happens in conventional disordered semiconductors, but highly dependent on its ionicity, which explains the very high mobilities (≥ 60 cm 2 V -1 s -1) achieved. The room temperature dependence of the Hall mobility on the carrier concentration presents a reverse behaviour than the one observed in conventional crystalline/polycrystalline semiconductors, explained mainly by the presence of charged structural defects in excess of 4 × 10 10 cm -2 that scatter the electrons that pass through them. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N- and p-type weakly absorbing and highly conductive microcrystalline thin μc-Six:Cy:Oz:H films, have been produced by a TCDDC (Two Consecutive Decomposition and Deposition Chamber) system1. The optoelectronic and structural results show that we are in the presence of a mixed phase of Si microcrystals (c-islands) embedded in a-Six:Cy:Oz:H (a-tissue). Based on that, we propose a model where transport mechanisms are explained by the potential fluctuations related to films heterogeneities. Thus, conduction is due to carriers that by tunneling or percolation "pass" or "go" trough the barriers and/or percolate randomly by the formed channels. © 1989.

This paper presents results of the role of the oxygen partial pressure used during the deposition process on the transport properties exhibited by doped microcrystalline silicon oxycarbide films produced by a Two Consecutive Decomposition and Deposition Chamber system, where a spatial separation between the plasma and the growth regions is achieved. This paper also presents the interpretative models of the optoelectronic behaviour observed in these films (highly conductive and transparent with suitable properties for optoelectronic applications) as well as the interpretation of the growth process that leads to film's microcrystallization.

This paper presents results of the role of the oxygen partial pressure (pO2) used on the properties exhibited by doped μc silicon oxycarbide films produced by a Two Consecutive Decomposition and Deposition Chamber (TCDDC) system [1], where a spatial separation between the plasma and the growth regions is achieved. The films produced are highly conductive and transparent with suitable properties for optoelectronic applications.

High quantum efficiency, UV-enhanced monocrystalline zinc sulphide optical sensors for precise radiometric and spectroscopic measurements have been developed by spray deposition of heavy fluorinedoped tin oxide thin films with carrier concentration near 1021 cm-3 onto the surface of zinc sulphide monocrystals as an alternative to the UV-enhanced silicon photodetectors as well as to new detectors based on SiC and GaN. The fabricated sensors have an unbiased internal quantum efficiency that was nearly 100% from 250 to 320 nm, and the typical sensitivity at 290 nm is 0.15 A/W. The sensors were insensitive to solar radiation in earth's conditions and can be used as solar blind photodetectors for precision UV-measurements under direct solar illumination, both terrestrial and space applications.

We report the architecture and the performances of a memory based on a single field-effect transistor built on paper able to write-erase and read. The device is composed of natural multilayer cellulose fibers that simultaneously act as structural support and gate dielectric; active and passive multicomponent amorphous oxides that work as the channel and gate electrode layers, respectively, complemented by the use of patterned metal layers as source/drain electrodes. The devices exhibit a large counterclockwise hysteresis associated with the memory effect, with a turn-on voltage shift between 1 and -14.5 V, on/off ratio and saturation mobilities of about 104 and 40 cm 2 V-1 s-1, respectively, and estimated charge retention times above 14 000 h. © 2008 American Institute of Physics.

This paper discusses the effect of order and disorder on the electrical and optical performance of ionic oxide semiconductors based on zinc oxide. These materials are used as active thin films in electronic devices such as pn heterojunction solar cells and thin-film transistors. Considering the expected conduction mechanism in ordered and disordered semiconductors the role of the spherical symmetry of the s electron conduction bands will be analyzed and compared to covalent semiconductors. The obtained results show p-type c-Si/a-IZO/poly-ZGO solar cells exhibiting efficiencies above 14% in device areas of about 2.34 cm2. Amorphous oxide TFTs based on the Ga-Zn-Sn-0 system demonstrate superior performance than the polycrystalline TFTs based on ZnO, translated by ION/IOFF ratio exceeding 107, turn-on voltage below 1-2 V and saturation mobility above 25 cm2/Vs. Apart from that, preliminary data on p-type oxide TFT based on the Zn-Cu-O system will also be presented. © 2009 SPIE.

A study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet (UV) photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process was presented. It was found that the film described were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films changed more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. Analysis shows that the porous and textured zinc oxide films produced by spray pyrolysis at low substrate exhibit an excellent ac impedance response.